Marsh A400 vs Bryston 4B-ST

Currently own a CLASSE model 6 preamp and PSB Stratus GOLD i
speakers. With price not being a factor what would be a
better match for a power amp. Marsh A400 or a Bryston 4B-ST? What are the differences or characteristics of the
two power amplifiers. Right now I have a Bryston 3B-ST and
I find that I need more power for the PSB's.
Given those choices, Bryston, for build quality and warranty. But, I have heard both, and I think you would be far better off with a used Classe 200, 201 or 300.
I have a Bryston 4B-ST, and it should have more than enough power to drive your Stratus Gold's. The Marsh A400 is rated at 200 wpc, while the Bryston 4B-ST is rated at 250 wpc. Both amps have fairly conservative ratings, however. The lab test measurement sheet that came with my 4B-ST indicated that my amp actually produced 294 wpc when it was bench-tested before leaving the factory. The 4B-ST typically produceds 290-300 wpc at 8 ohms, 20-20K Hz.
What is most critical in your decision is the interaction between the speaker and the amplifier. I own a 4B-ST and love it. And I am also an active proponent of the Bryston 20 year warranty (noted above) as well as the exceptional service and overall customer support provided by Bryston. As you may know, Bryston's resale value is also quite good. I also own a BP-25 preamp, and as others have indicated, there is something of a synergistic relationship between the amp and the preamp. Certainly, the combination is dead quiet. I can place my ear right next to the speaker and there is absolutely no hum or buzz. And the overall sound is accurate and dynamic and pleasant to listen to, without any trace of harshness. Prior to purchasing, I investigated both the A400 and the 4B-ST since we have no local authorized dealer for either brand within at least 400 miles. In so doing, I spoke to representatives of both manufacturers as well as a few authorized dealers. Ultimately, I selected the 4B-ST because of its ability to more easily drive lower impedance loads. In that respect, Bryston told me that it is more similar to the 7B-ST than the 3B-ST. The present iteration of the A400 is not as comfortable with lower impedance loads, a fact that I was informed of by the manufacturer. However, a dealer told me that a higher current version of the amplifier may be available sometime this year. Also, do not forget that Marsh can be purchased factory-direct if you have no local dealer; and there is provision for an in-home trial period.
In a direct comparison that I heard the Marsh sounded more musical and detailed. It also sounded subjectively like it has more power. The Bryston, of course, has the better warranty.
I was considering a Marsh but then found that they are made in Taiwan, that is all I am going to say about that.
I have listened to both amps and for my ears I have purchased the Marsh. It is a wonderful amp for the money.
I don't care where the amp was made. After I had a peek under the hood at a local dealer I was impressed at the build quality and calibre of parts used in the amp. You could spend much more and do alot worse. The Bryston is a fine amp with the best warranty and built like a tank. Sonically, I felt the Marsh was better and I drive some hard to drive electrostatics. Listen to both and let your ears decide.
If it is warranty and build quality you are after...i'd have to say go with the Bryston. If you want the best sound (as did I) go with the Marsh!!